The present invention relates to automotive vehicle brake lathes configured for resurfacing brake rotor components, and in particular, to an improved on-car brake lathe apparatus and a method for compensating for runout between an on-car brake lathe and a vehicle wheel hub to which the on-car brake lathe is secured for a brake rotor resurfacing operation.
One of the main components of a vehicle wheel braking system employing disc brakes are the brake rotors, which provide a solid rotating surface against which the stationary brake friction pads are clamped or compressed to generate a frictional force, slowing the rotational movement of the brake rotors and the associated vehicle wheels. The brake rotors are subjected to frequent and substantial frictional forces by the brake friction pads, and over time, become worn. Uneven application of braking force, debris, or uneven frictional surfaces on the brake friction pads can result in the formation of grooves, channels, or scratches in the surfaces of the brake rotors. Repeated heating and cooling of the brake rotors resulting in extreme temperature variations can additionally result in a lateral warping of the brake rotors.
A worn or warped brake rotor may be resurfaced by cutting or grinding to provide a uniform smooth brake friction pad contact surface if sufficient brake rotor material remains to provide an adequate braking surface without compromising the structural integrity of the vehicle braking system. However, once a brake rotor has been worn below a minimum safe thickness, it is unable to safely dissipate the heat generated during brake application, and must be replaced.
To provide for a uniform surface, any abnormalities in the brake rotor, such as a lateral warping, must be removed during the resurfacing procedures. Additional sources of lateral warping defects in a brake rotor include over tightened attachment bolts or uneven mounting surface onto which the brake rotor is secured in the vehicle wheel assembly. If the brake rotor is removed from the vehicle wheel assembly for a resurfacing operation on a fixed or “bench” brake lathe, any abnormalities or defects resulting from the mounting of the brake rotor to the vehicle wheel assembly may not be accurately identified or corrected during the resurfacing procedure. Accordingly, a variety of brake resurfacing machines or brake lathes have been developed to resurface brake rotors while they remain mounted to the vehicle wheel assembly.
Brake resurfacing machines or brake lathes configured to resurface brake rotors mounted to a vehicle wheel assembly are commonly referred to as on-car brake lathes. Examples of an on-car brake lathe include the OCL-series brake lathes sold by Hunter Engineering Co. of St. Louis, Mo. By eliminating the need to remove the brake rotor from the vehicle wheel assembly, the overall efficiency of the resurfacing procedure is improved, and the chances for operator induced error are reduced. However, the resurfacing of brake rotors which remain mounted to the vehicle wheel assembly requires that the on-car brake lathe and the vehicle wheel assembly, including the brake rotor, be aligned for rotation along a common axis, typically, the rotational axis of the vehicle wheel assembly hub onto which the on-car brake lathe is secured.
Often, the hub surface to which the vehicle wheel assembly mounts is not aligned within a required tolerance to the axis of rotation for the axle upon which the vehicle wheel assembly is secured. This deviation between the hub surface and the axis of rotation for the wheel assembly is referred to as lateral, or axial, runout, or axis misalignment, and must be compensated for either manually or automatically before beginning the resurfacing procedures with the on-car brake lathe.
Some manual runout compensation procedures are tedious and complex. First, an operator secures the output spindle of the on-car brake lathe to the vehicle wheel hub using a suitable adapter. Next, a motor in the on-car brake lathe is activated to rotate the output spindle, the adapter, and brake rotor. Any runout present in the system is directly measured by one or more measurement devices, which provide the operator with a suitable visual indication representative of the actual runout experienced by the on-car brake lathe as the adapter is rotated through one or more complete rotations. Using the visual indication, the operator manually adjusts one or more mechanical adjustment elements, such as screws or dials, altering the rotational axis of the on-car brake lathe output spindle to reduce the observed runout to within an acceptable tolerance for performing the resurfacing of the brake rotor.
To reduce the observed runout to within the desired tolerances using the manual runout compensation procedure usually requires several iterations when carried out by a skilled operator. The extra time spent by an operator to setup the on-car brake lathe and perform the manual runout compensation can substantially increase the time required to complete a brake rotor resurfacing, resulting in a corresponding increase in cost and lost productivity.
Accordingly, a number of on-car brake lathe devices have been configured with active automatic runout compensation mechanisms which do not require significant operator input. One such active automatic runout compensation mechanism is shown in U.S. Pat. No. 6,101,911 to Newell et al. The automatic runout compensation mechanism shown in the '911 Newell et al. patent includes at least one adjustment rotor interposed between a pair of adapters and which is concentric about an axial drive shaft. The on-car brake lathe motor and cutting elements are secured to one adapter, and the entire mechanism secured to the vehicle wheel hub via the second adapter. The adjustment rotor includes a slanted surface in engagement with either a second adjustment rotor having an opposing slanted surface or one of the adapters. An adjustment mechanism is utilized to alter the rotational orientation of the adjustment rotor about the axis of the axial drive shaft.
As the components of the '911 Newell et al. automatic runout compensation mechanism are rotated about the axis at a fixed speed, runout is detected by an accelerometer. A processor receives an output signal from the accelerometer and provides corresponding control signals to an adjustment mechanism. Alteration of the rotation position of the adjustment rotor about the axis of the axial drive shaft as the components are rotated attempts to compensate for the detected runout by altering the angle at which the two slanted surfaces are engaged, and correspondingly the angle between the first and second adapters. After each angle alteration, the runout is observed to determine if it has increased or decreased, leading to further adjustments. Due to significant high speed vibrations and the interaction of the various rotating components, such as bearings, gears, and shaft, errors are induced in the automatic runout compensation sensor signals. Thus, automatic runout compensation typically requires several complete rotations of the various components about the axis and adjustments before the adjustment rotor rotational position is sufficiently altered to compensate for any detected runout.
The automated adjustment mechanism of the '911 Newell et al. patent associated with the use of the one or more slant rotors is a costly and complex mechanical arrangement. The mechanism requires a lengthy trial-and-error adjustment process to compensate for any detected runout.
Accordingly, there is a need for on-car brake lathes having improved precision runout compensation mechanisms, which are not subjected to rotational movement noise and vibrations during runout measurements, and which can quickly and accurately compensate for detected runout by directly aligning a pair of slant rotors to a target orientation without a trial-and-error adjustment process.
It is further desirable to create a brake resurfacing system that will detect when a rotor resurfacing cut is completed and automatically stop the operation of the brake lathe, thereby reducing the time required for the operator to prepare the brake lathe to resurface the next rotor.